As for mobile communication terminal manufacturers, they need to determine an actual call voice quality of their manufactured terminal for manufacturing a high quality terminal. As for mobile communications carriers, they also need to determine an actual call voice quality for a purpose of an optimization by checking a performance or a state of self-managing and self-maintaining a mobile communications network. Mean opinion score (MOS) is proposed as a method of measuring the above-described call voice quality.
The MOS is a subjective method of measuring a sound quality evaluated in 5 different ratings as shown in Table 1 by scoring satisfaction scales from users and then finding an average value while having multiple users hearing an actual call voice
TABLE 1MOS ValueQuality Rating5Excellent4Good3Fair2Poor1Bad
As described above, since the MOS measuring method having a lack of objectivity and a high measuring cost is a subjective measuring method by a user, automated and objectified methods are preferred recently, which are specifically the perceptual speech quality measurement (PSQM) algorithm defined on P.861 of the ITU-T and a perceptual evaluation of speech quality (PESQ) standard as an algorithm defined on P.862 based on the PSQM algorithm for corresponding to a packet loss or the like.
Meanwhile, as a Voice over IP (VoIP) or Voice over LTE (VoLTE) is being commercialized, audio data is also transmitted in a packet form. Every packet is not always sequentially transferred to a destination due to a characteristic of a packet switching network and a delay frequently occurs based on a network environment. Thus, the delay has emerged as a very important item in an MOS measurement of VoIP or VoLTE system.
In accordance with an embodiment of the conventional method, the MOS measuring device has at least two ports in which an original audio file, for example an original WAV file, is replayed through one port, and an audio file received through an IP network or LTE network is recorded through another port while connecting each of the mobile communication terminals to the MOS measuring device, and a CPU for a control and a CODEC are included in each port. Meanwhile, each port is connected to a data pin and an audio jack of the mobile communication terminal through a USB cable and an audio cable. In this case, a host program for a control of the CODEC included in each port, that is, for a control of replaying and recording the original WAV file, is loaded in the mobile communication terminal.
Hereinafter, the ports used for the replaying and the recording are referred to as a “replaying part” and a “recording part” for the sake of convenience, respectively, and the mobile communication terminals used for the replaying and the recording are referred to as a “replaying terminal” and a “recording terminal”, respectively.
In a conventional MOS measuring device having the above-described configuration, when an original WAV file is replayed and output to the replaying terminal through the CODEC of the replaying part, the audio signal is received in a packet form through an IP network or LTE network by the recording terminal connected to the recording part. The audio signal received by the recording terminal is recorded after decoding through the CODEC included in the recording part and comparing with the original WAV file, and then used in measuring a call quality, a call delay time, or the like.
According to the above-described conventional MOS measuring device, while an operator executes a host program of the replaying terminal and the recording terminal, the MOS measurement is eventually started by manually pressing a “replay” button through the replaying terminal and manually pressing a “record” button through the recording terminal at the same time.
However, according to a synchronizing method by the conventional manual operation as described above, since simultaneously pressing the “replay” button and the “record” button within a time range of tens of milliseconds is difficult, measurement of the actual call delay time is difficult. In addition, since measured values differ by operator or every measuring time, there is a problem in which measurement reliability is degraded.